In recording or reading information on a moving information storage media, such as magnetic recording, relative motion between the record/read head and the storage or recording media is required. The relative velocity between the head and media interface may be, for example, 550 IPS for video and high density digital applications. To achieve maximum performance, there must be an interface of intimate contact between the record/read head and the media surface without destruction or excessive wear of the magnetic field responsive coating on the recording media.
As contact pressure between the head and media is increased to improve performance, both media and head wear are increased. The problem is particularly severe in video applications and compounded where the media is utilized for storing single video frames on separate tracks of a magnetic disc wherein the single tracks are continuously in contact with the head to provide continuous stationary displays of the single frames. In only five minutes of play time revolving at 3600 RPM, for example, a track on the disc is scraped about eighteen thousand times by the head. The wear products are so hard and abrasive that they are commonly used as lapping compounds. Thus, intimate contact very rapidly abrades the track and the magnetically stored information is destroyed.
To prevent failure caused by contact between the head and disc, lubricated surfaces and/or air film separations have been used. However, any separation between the head and disc caused by such lubricating fluid or air film imposes a loss of signal and hence performance. This spacing loss is equal to about 54.6 d/.lambda. dB where d is the head/disc separation in inches and .lambda. is the recorded wavelength in inches. Thus, a head/disc separation equal to the wavelength would cause about a 54.6 dB loss in the output of the replay head. Since it is desired to record wavelengths that approach 70 .mu.-in., the playback head voltage is reduced by 50% by only 7.7 .mu.-in. of separation. On the other hand, as discussed above, reduction of separation to meet desired performance would cause the interface to be destroyed within a few seconds.
Prior art solutions to the head to disc interface problem have generally been of two types: flying heads in conjunction with rigid hard-plated discs, and heads having large surface areas buried in soft flexible "floppy" discs. Utilizing the first technique of flying heads on a large plated disc requires a rigid substrate, usually aluminum, covered by a magnetic field responsive material such as nickel cobalt plated to a thickness of about 10 .mu.-in. and covered by about 5 .mu.-in. of plated rhodium for wear protection. Aside from the fact that these discs are very expensive, in order to prevent excessive wear, the record head is required to fly on a cushion of air when the disc revolves at full speed. The head to disc separation is usually between 35-50 .mu.-in. The delicate balance of forces which keep the head flying above the surface utilizing this technique can be disturbed by minute dust particles or fingerprints which may cause the head to catastrophically crash into the disc. Consequently, the disc cannot be handled without gloves, is ordinarily handled in a special clean room environment, and is usually sealed within an evacuated container. By increasing the flying height, head crashes are less prevalent, but separation then prohibits performance except for low frequency digital applications. Thus, as seen from the above description, flying heads on rigid discs is nonsuitable for low cost, high volume consumer applications such as video recordings.
The flexible or so-called "floppy" disc reduces the handling and cost problems realized in the above rigid disc system. Until now, however, record/read heads for floppy discs were relatively large to provide an interface comprised of the large contoured head buried in the soft flexible media. The large record/read head surface area distributes the force per unit area to reduce media wear and separation loss. As the media is moved past the head, however, air will collect between the head and disc surface to form a film. The thickness of this air film is a function of media tension, head surface radius, viscosity of the air, and disc head relative velocity which may be approximated by the function h (air film thickness) = 0.642R [6 .mu.v/T].sup.3/2 where R is the head profile radius, v is the relative velocity, T is the media tension and .mu. is the viscosity of air. Accordingly, most flexible or "floppy" disc applications are limited to slow speed, low bandwidth digital computer applications. The performance penalty realized by the prior art has precluded the use of a flexible or "floppy" disc interface for wide bandwidth or video type applications.
It is therefore an object of the present invention to provide an improved technique for storing information on a flexible storage media.
Another object of the invention is to provide an improved system for magnetically storing information on a flexible magnetic recording disc.
A further object of the invention is to provide an apparatus which permits the continuous long-term reproduction of wide bandwidth signals from a flexible magnetic storage disc without excessive wear to the record surface of the disc or the record head and without sacrificing performance.
Still another object of the invention is to provide a flexible information storage media with tension and stability as well as compliance and resilience.
A still further object of the invention is to provide an apparatus which includes a flexible magnetic storage disc which permits a high performance narrow track video record head to be used in contact with the magnetic disc.
It is another object of the invention to provide an apparatus which permits the recording and reproducing of a wide bandwidth signal such as a video signal utilizing an inexpensive flexible particulate type recording media.
It is another object of the invention to provide an apparatus in which a head-to-disc interface is provided which is capable of recording wavelengths of 1.2 mils to 70 .mu.in. without significant separation loss at a low relative velocity of, for example, 150 IPS.
It is another object of the invention to continuously reproduce slow speed recorded signals for a long time at a much higher relative velocity of, for example, 550 IPS without significant head or media wear.
It is still another object of the invention to use the same media and media supporting and stabilization apparatus for both record and replay of flexible discs.
It is another object of the invention to provide an apparatus which permits reproduction of RF frequencies of 450 KHz to 6.5 MHz at 550 IPS on the same track for up to 10 hours without deleterious separation losses.
It is another object of the invention to provide an apparatus which is able to record and replay within 0.1 in. of the outer edge of a flexible disc.
It is still another object of the invention to provide an apparatus with rotation of the disc as a free form without additional tensioning apparatus or rotating plates for stabilization.
Another object of the invention is to continuously replay a flexible magnetic storage media while maintaining an air-bearing between the replay head and media regardless of head loading.
A further object of the invention is to provide a complaint, but resilient, magnetic recording surface capable of withstanding shock, vibration and head "crashes" without media degradation.
A still further object of the invention is to provide stable record or playback of a flexible storage media while it is in rotation in any plane, including upside down.
These and other objects and advantages are provided in accordance with the present invention in which an apparatus is provided for recording and/or reading information on the upper major surface of a flexible information storage media such as a flexible disc. The apparatus which may be in the form of a cartridge is comprised of a body having a cylindrical surface wherein the flexible media is rotated over the cylindrical surface with the lower major surface of such media facing the cylindrical surface so that rotation of the media causes the media to conform to the curvature of the body. A recording and/or playback head is selectively passed or indexed over the upper major surface of the disc for reading and/or writing information on the media as it rotates. In one embodiment of the invention, the cylindrical surface is comprised of a spring-flexible material such as plastic which gives slightly as the media rotates over the surface. In another embodiment of the invention, the media is comprised of a flexible plastic disc having a magnetic flux responsive layer adherently formed on the upper major surface thereof.